This the third Thread where you are asking about this same RIAA output.
Why are you spreading all your questions around the Forum?
Why are you spreading all your questions around the Forum?
Sorry, I directed the previous post [ http://www.diyaudio.com/forums/pass-labs/181552-b1-preamp-build-thread-32.html#post5074546 ] to this one because I lately realized that that was not the right thread to ask.
Thanks for your answering on the other post,
Reagards
Pierre
PS: my reply to your point in the previous post is: I don't have cable connection is within the same chassis.
Am slightly confused on the question of twisted pairs to output. Generally, twisted pairs help with RFI rejection, but can also increase capacitance which could be an issue for a passive. Yet the b1 buffer is meant to increase driving capacity. Routing of hookup wire also will affect RFI. So... some people don't twist, others do. Have I got these issues wrong?
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The signal wires must be close coupled. You can choose coaxial or twisted pair for these close coupled wire pairs.
A parallel pair of wires, as used in standard speaker figure of eight and two core mains cable emit too much emi.
The twisting helps a lot in attenuating the emi, due to cancelling effect of opposite phases of the interference.
For good examples of twisting to reduce interference look critically at balanced microphone cable and CAT5/6/7 cables.
A parallel pair of wires, as used in standard speaker figure of eight and two core mains cable emit too much emi.
The twisting helps a lot in attenuating the emi, due to cancelling effect of opposite phases of the interference.
For good examples of twisting to reduce interference look critically at balanced microphone cable and CAT5/6/7 cables.
Right, that's consistent with what I thought. And an argument from silence says that you don't find capacitance a relevant issue in regards to signal wires?
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Linear pot vs. logarithmic
On the Passdiy it is stated that it uses a 25k linear taper potentiometer. Why linear? Would a log taper do the job (because I have them in my diy stock)?
On the Passdiy it is stated that it uses a 25k linear taper potentiometer. Why linear? Would a log taper do the job (because I have them in my diy stock)?
log works and tries to give similar attenuation for each rotation increment.
but the manufacture of log post has much increased error/tolerances.
This leads to variations in balance between channels and a smaller variation of slope at different rotations.
Linear is more consistent, but has poor sensitivity at higher attenuations. Down to about 10% (-20dB) or 15% (-16.5dB) of electrical rotation you can experience good sensitivity. Below that they are pretty poor. If you have your system gain set up so that you never need high attenuations, then a linear law vol pot will probably feel very acceptable.
but the manufacture of log post has much increased error/tolerances.
This leads to variations in balance between channels and a smaller variation of slope at different rotations.
Linear is more consistent, but has poor sensitivity at higher attenuations. Down to about 10% (-20dB) or 15% (-16.5dB) of electrical rotation you can experience good sensitivity. Below that they are pretty poor. If you have your system gain set up so that you never need high attenuations, then a linear law vol pot will probably feel very acceptable.
Capacitance only becomes a concern when the Source is incapable of driving the load. i.e. the combined paralleling of cable capacitance and Receiver impedance+RF filtering.
You sort the source, not corrupt the cable.
Twisting only matters if you are having noise problems before you twist. If you have some humm, buzz, static then twist. This MAY solve the problem. Untwisted wires do not create noise they just catch it and if one catches more than the other then that shows up on the output. So you would need a source of noise for twisting to solve anything.
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Well I suppose if you don't twist something like power transformer wires then you could get some noise into the air to be picked up elsewhere and if they were all twisted then you would send out a negative and positive copy of that noise which would cancel out. Again if they're is no noise present then there is no problem to fix.
B1 is not a passive pre. It is active with gain close to one.
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A signal pair when untwisted act as an aerial and will emit emi if any non constant current passes around the loop. (Pure noisless DC cannot create emi. It just creates a constant magnetic field. It is a changing magnetic filed that is the emi).
The bigger the aerial loop the bigger the emitted emi, (subject to avoiding the resonance of an intended aerial).
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I know I should read the entire thread and I have begun reading it, but here is a quick question if anyone could pl answer.
would a basic LM317 supply (as per datasheet) be ok for B1 ckt as designed by Mr. Pass (single supply)? I plan to incorporate it on the buffer pcb itself for reducing wiring.
regards
Prasi
would a basic LM317 supply (as per datasheet) be ok for B1 ckt as designed by Mr. Pass (single supply)? I plan to incorporate it on the buffer pcb itself for reducing wiring.
regards
Prasi
I ran mine that way for a while before I switched to a shunt supply. It worked fine. Be sure to use an oversized transformer - it makes a difference, in my experience.
Given this circuit has a projected current draw of 200mA max, as I recall, how much over spec'ing are you talking about? I was thinking of a 20VA transformer which should provide 800mA.
...of course there is also the current draw of the power supply itself, which mine should be around 50mA. I assume a shunt's draw might be a good bit more.